experimental research on beneficiation of typical fluorite ore in wuling mountain ind miner process 2015 6 13 15

flotation studies of fluorite and barite with sodium petroleum sulfonate and sodium hexametaphosphate - sciencedirect

flotation studies of fluorite and barite with sodium petroleum sulfonate and sodium hexametaphosphate - sciencedirect

The development of new collectors to separate fluorite from barite is urgently needed in mineral processing. In this study, the flotation behavior of fluorite and barite was studied using sodium petroleum sulfonate (SPS) as a collector with sodium hexametaphosphate (SHMP) as a depressant. The performance of reagents on minerals was interpreted by infrared spectroscopic analysis and zeta potential measurement. The flotation results showed that SPS performed well in a wide pH region (711) even at a low temperature (5C), while the flotability of fluorite and barite were almost the same. At pH 11, the presence of SHMP obviously depressed fluorite rather than barite and SHMP exhibited good selective inhibition to fluorite. Fourier-transform infrared spectra and zeta potential results showed that: (1) SPS can adsorb on fluorite and barite surfaces and (2) SHMP had little effect on the adsorption of SPS on a barite surface, although it interfered with the adsorption of SPS on a fluorite surface through strong adsorption.

a review of reagents applied to rare-earth mineral flotation - sciencedirect

a review of reagents applied to rare-earth mineral flotation - sciencedirect

The rare-earth elements (REE), which encompass the fifteen metallic elements of the lanthanoid series of the periodic table, yttrium and occasionally scandium, have gained enormous public, economic and scientific attention in recent years. These elements, which have been found in over 250 minerals, are of high economic and strategic importance to many high-technology industries. As such they have been designated as critical materials by several countries and many new deposits are being developed. Rare-earth mineral (REM) deposits can be broadly classified into four geological environments: carbonates, alkaline/peralkaline igneous rocks, placers and ion adsorption clays. Apart from ion adsorption clay deposits, which require no mineral processing steps, froth flotation is the most applied beneficiation technique. This paper reviews the flotation of REM, covering their surface chemical properties as well as the various flotation reagents which have been employed.

production of mixed rare earth oxide powder from a thorium containing complex bastnasite ore - sciencedirect

production of mixed rare earth oxide powder from a thorium containing complex bastnasite ore - sciencedirect

The production of mixed rare earth oxide powder from a thorium containing bastnasite ore was investigated.92.6% La, 86.8% Ce, 86.9% Pr, 82.3% Nd, 95.4% Th and 31% Y were extracted by acid bake-water leach process.99.8% Ce, 99.7% La, 97.3% Nd, 98.1% Pr, 91.7% Y and 97.4% Th were co-precipitated by oxalic acid.The final product contains 88.54% REO and 6% ThO2.The REO powder has an irregular crystal shape.

The production of mixed rare earth oxide powder from a thorium containing bastnasite ore by sulfuric acid bake-water leaching followed by precipitation with oxalic acid and thermal decomposition of the oxalates was investigated. The sulfuric acid baking was performed at 250C and the optimum baking time was found to be 3h. Using deionized water as lixiviant, 92.6% La, 86.8% Ce, 86.9% Pr, 82.3% Nd, 95.4% Th and 31% Y were dissolved from the baked ore at 25C after 30min of leaching. The effect of solid-to-liquid ratio on the dissolution of the rare earth elements and thorium shows that when the solid ratio in the water increased from 1:10 to 1:3, the dissolution percentage decreased. The final mixed rare earth oxide powder contained 88.54% REO and 6% ThO2 together with small amounts of other impurities. The SEM mapping results revealed that the produced REO has an irregular crystal shape. Based on the experimental results obtained from the current study, a flowsheet was proposed for the production of mixed rare earth oxide powder from a specific complex bastnasite ore.

minerals | free full-text | mineral processing and metallurgical treatment of lead vanadate ores | html

minerals | free full-text | mineral processing and metallurgical treatment of lead vanadate ores | html

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thermodynamic mechanism analysis of calcification roasting process of bastnaesite concentrates | springerlink

thermodynamic mechanism analysis of calcification roasting process of bastnaesite concentrates | springerlink

A novel calcification roasting decomposition method for bastnaesite concentrates has been proposed previously. In this work, the thermodynamic mechanism was investigated via simultaneous measurements of thermogravimetry and differential thermal analyses, combined with X-ray diffraction analyses. Rare earth oxides and calcium fluorides were generated after bastnaesite and calcium hydroxide broke down, respectively. The generation and decomposition of calcium carbonate occurred at the same time. Considering the difficulties in obtaining pure substances, theoretical calculations were applied to determine the standard enthalpy of formation (f H 298), Gibbs free energies of formation (f G 298), and heat capacities at constant pressure (C p) of some rare earth minerals (CeFCO3 and CeOF). Based on these results, the standard Gibbs energy of reaction at different temperatures (r G T) was ascertained, and the major reactions were verified to be thermodynamically reasonable.

Cen, P., Wu, W. & Bian, X. Thermodynamic Mechanism Analysis of Calcification Roasting Process of Bastnaesite Concentrates. Metall Mater Trans B 48, 15391546 (2017). https://doi.org/10.1007/s11663-017-0951-7

review on hydrometallurgical recovery of rare earth metals - sciencedirect

review on hydrometallurgical recovery of rare earth metals - sciencedirect

Review on hydrometallurgical recovery of rare earth metals from various resourcesVarious leachants used to recover rare earths from primary and secondary resourcesSolvent extraction studies using cationic, anionic, chelating, etc. extractantsSeparation of rare earth metals from chloride, nitrate, phosphate, etc. solutions

Rare earth metals are essential ingredients for the development of modern industry as well as designing and developing high technology products used in our daily lives. Consequently, the worldwide demand of rare earth metals is rising quickly and predicted to surpass the supply by 40,000tons annually. However, their availability is declining, mainly due to the export quotas imposed by the Chinese government and actions taken against illegal mining operations. This has laid emphasis to exploit and expand technologies to meet the future necessities of rare earth metals. Bastnasite, monazite, and xenotime are their chief mercantile sources, which are generally beneficiated by flotation, gravity or magnetic separation processes to get concentrates that are processed using pyro/hydrometallurgical routes. To develop feasible and eco-friendly processes, R&D studies are being conducted for the extraction of rare earth metals from leached solutions (chloride, nitrate, sulfate, thiocyanate, etc.) using different cationic, anionic and solvating solvents or ions depending on material and media. Commercial extraction of rare earth metals has been carried out using different extractants viz. D2EHPA, Cyanex 272, PC 88A, Versatic 10, TBP, Aliquat 336, etc. The present paper reviews the methods used for the recovery of rare earth metals from primary as well as secondary resources, with special attention to the hydrometallurgical techniques, consisting of leaching with acids and alkalis followed by solvent extraction, ion exchange or precipitation. The piece of comparative and summarized review will be useful for the researchers to develop processes for rare earth recovery under various conditions.

selective flotation separation of bastnaesite from calcite using xanthan gum as a depressant - sciencedirect

selective flotation separation of bastnaesite from calcite using xanthan gum as a depressant - sciencedirect

Selective flotation separation of bastnaesite (B) from calcite (C) was realized.Xanthan gum (XG) was used as a depressant and sodium oleate as a collector.XG interacted with Ca ions on C surface in preference to rare earth ions on B surface.XG adsorption on the surface of C suppressed oleate ion adsorption thereon.

The inability of rare earth and gangue minerals to be efficiently separated by flotation due to their similar physicochemical properties is a major challenge of the rare earth industry. Bastnaesite is one of the principal sources of light rare earth elements. The use of traditional flotation reagents often poses the problem of poisonous wastewater generation. Therefore, we use xanthan gum (XG) as a non-toxic, biodegradable, and cheap depressant to selectively separate bastnaesite from calcite by flotation and probe the corresponding mechanism. Microflotation experiments/zeta potential measurements conducted with/without XG using sodium oleate as a collector demonstrate that at pH 8, XG decreases the flotation recoveries of calcite and bastnaesite by 85.09 and 22.37%, respectively. Further analysis of adsorption behaviour on the mineral surface and possible reagent-mineral interactions shows that selective mineral separation is due to the preferential interaction of XG with Ca ions on the calcite surface and the suppression of oleate ion adsorption thereon due to the steric hindrance of polymeric XG. Hence with regard to the potential of XG in calcium-bearing mineral separation, XG could be as a new depressant for RE mineral flotation.

the rare earth element (ree) mineralisation potential of highly fractionated rhyolites: a potential low-grade, bulk tonnage source of critical metals - sciencedirect

the rare earth element (ree) mineralisation potential of highly fractionated rhyolites: a potential low-grade, bulk tonnage source of critical metals - sciencedirect

The rare earth elements (REE) have become crucial for modern industry, technology and medicine, with the increase in demand for these elements over the past few years currently being met by relatively few well-known mineral deposits. This lack of a secure supply of the REE has led to increased research into potential alternative sources of these in demand elements. The primary fractionation processes involved in the petrogenesis of highly fractionated high-silica rhyolites can cause the magmas that form these units to become preferentially enriched in the REE, especially in the more valuable heavy REE (HREE), although this is dependent on the mineral assemblages fractionated by the system in question, a factor that is in turn a function of the source and tectonic setting of a given magmatic event. The mineralogy of the REE is also important, with volatile exsolution and vapour-phase activity within highly evolved rhyolite systems potentially having a key role in concentrating the REE and other elements into concentrations (and more importantly potentially acid leachable and therefore processable minerals) that may be economically viable to extract. This, combined with the fact these rhyolites are often enriched in other critical and/or economically important metals (e.g., Y, Nb, Ta, Be, Li, F, Sn, Rb, Th, and U) means that these volcanic units should be considered as potential sources of these critical metals. In addition, the large volume nature of these rhyolites combined with the fact they frequently crop out at the Earths surface makes them ideally suited for more economical bulk open pit extraction. This suggests that these high-silica REE-enriched rhyolites should be considered potential REE analogues of bulk-tonnage, low-grade porphyry Cu deposits, warranting further investigation to determine whether these rhyolites are a viable new source of the REE (especially the HREE) and are potential targets for future mineral exploration.

The global demand for the rare earth elements (REE) has increased significantly during recent decades, as these elements have crucial uses in integral parts of modern technology, including uses in alloys, magnets, batteries, and glass during the manufacturing of computers, magnets, lasers, and screens and in petroleum refining and as catalysts (Haxel et al., 2005, Maestro and Huguenin, 1995, Weng et al., 2013, Weng et al., 2015, Du and Graedel, 2011, Du and Graedel, 2013; Fig. 1). This has driven exploration for both traditional sources of the REE (e.g., carbonatites, including the worlds largest REE resource at Bayan Obo, Inner Mongolia, China and important REE mineralisation at Mountain Pass, California, USA; Drew et al., 1990, Olson et al., 1954, Smith et al., 2015, Verplanck et al., 2016, Yang et al., 2011, Weng et al., 2015) and the identification of other unconventional sources of the REE. Although carbonatite-hosted REE deposits have dominated the supply of these elements for the past 50years (Haxel et al., 2005, Weng et al., 2013), these deposits are high grade (e.g., 56wt% REE2O3 at Bayan Obo; 9wt% REE2O3 at Mountain Pass; McLennan and Taylor, 2013) but (with the notable exception of Bayan Obo) are generally small (e.g., Mountain Pass, with 16.7 Mt of resources, Mt. Weld, with 23.9 Mt of resources; Weng et al., 2013, Weng et al., 2015). More importantly, these carbonatites have REE assemblages that are dominated by the light REE (LREE) and contain only small amounts of the rarer and higher priced heavy REE (HREE). However, price and rarity is not the entirety of this story, as although the criticality of a given element is dependent on end-user viewpoint (e.g. Jowitt, 2016, Sykes et al., 2016) it is generally agreed that the magnet REE (e.g. Nd, Dy, Pr) and those used in phosphors are the most critical of these elements (e.g., Nassar et al., 2015). This means that understanding the abundances of these differing elements within highly evolved rhyolitic systems is a key step in terms of addressing their prospectivity as sources of the REE. It should also be noted that the global mining industry often uses a slightly different classification than the IUPAC (2005) classification of the REE with Pm, Sm, Eu, Gd and Y (not strictly a REE) included with the HREE (Weng et al., 2013); as such, and given the mineral exploration focus of this paper, we omit Y from total REE (TREE) concentrations and report it separately (where possible) and define the following in this study: LREE (La, Ce, Pr, Nd) and HREE (Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu).

This study focuses on a new potential source of the REE (and potentially more importantly the HREE): highly fractionated high-silica rhyolites. These rhyolites are exemplified by the Round Top Mountain rhyolite in Texas, USA, a deposit that contains 1.03 Bt of resources at a total REE (TREE) grade of 305ppm (+220ppm Y), is enriched in the HREE relative to the continental crust, and contains resources that can be extracted by relatively simple leaching (Hulse et al., 2013, Pingitore et al., 2014, Weng et al., 2015). A number of other REE-enriched but under-explored rhyolites have also been identified; this study outlines the potential for these rhyolites to be the REE equivalents of low grade porphyry-Cu deposits, with their significant volumes meaning they have potential for the large-scale extraction of the REE by bulk tonnage, low grade extraction methods. The magmas that form these rhyolites are generated by long-lived fractionation, a process that can concentrate the REE in melt fractions within magmatic systems (depending on the compatibility or incompatibility of these elements within the minerals being fractionated, e.g. Miller and Mittlefehldt, 1982), with these melts then being erupted or emplaced to form highly fractionated and REE-enriched rhyolites (Chakhmouradian and Zaitsev, 2012). Importantly, these highly fractionated rhyolites can become preferentially enriched in the HREE relative to the LREE as a result of either extreme fractionation (Miller and Mittlefehldt, 1982) and/or late-stage magmatic upgrading and potential vapour phase crystallisation (Price et al., 1990, Agangi et al., 2010). The comparative lack of global resources for the HREE and the higher prices of some of these elements relative to the LREE means these rhyolites should be considered highly prospective future sources of the REE; in addition, these rhyolites are often enriched in other critical elements such as Y, Mo, Nb, Ta, Be, Li, Cs, F, Sn, Rb, Th and U, making them even more attractive exploration targets (Castor and Hedrick, 2006, Chakhmouradian and Wall, 2012, Hatch, 2012). This study provides an overview of these rhyolites, outlines potential problems associated with the extraction and processing of these deposits, comments on a potential mineralogical barrier for REE mineralisation within these rhyolites, and outlines a number of areas requiring future research.

Highly fractionated rhyolites generally contain >70wt% SiO2 and are typically enriched in the REE and lithophile elements relative to crustal abundances (e.g., Rudnick and Gao, 2003). They occur as rheomorphically welded or lava-like ignimbrites (e.g., the Kathleen Ignimbrite; Medlin et al., 2015), lavas (e.g., Glass Mountain; Metz and Mahood, 1991), domes (e.g., Taylor Creek Rhyolite; Duffield and Dalrymple, 1990), and intrusions (e.g., Round Top Mountain; Price et al., 1990) within bimodal

The most important of the potentially REE prospective rhyolites is the Round Top Mountain rhyolite deposit in Texas, USA (Price et al., 1990, Price, 2004, Hulse et al., 2013; Fig. 2). This deposit is one of five Sierra Blanca rhyolite laccoliths in the trans-Pecos area of Texas (e.g., Price et al., 1990) and the only rhyolite-hosted REE deposit to date with a NI43-101 compliant resource (Hulse et al., 2013). The deposit is currently owned by Texas Rare Earth Resources Corporation (Weng et al.,

The Mesoproterozoic 10715Ma Kathleen Ignimbrite (KI) of the west Musgrave Province of Western Australia (Fig. 2) and the associated Rowland Suite (RS) are both evolved, A-type, metaluminous (to slightly peraluminous) high-silica rhyolites with elevated REE concentrations (e.g., maximum of 794ppm TREE+200ppm Y with 23ppm Yb; Medlin, 2014, Medlin et al., 2015) relative to crustal abundances (e.g., Sun and McDonough, 1989, Wedepohl, 1995, Rudnick and Gao, 2003). These rhyolites formed during a

There are a number of global occurrences (Fig. 2) of large-volume high-silica rhyolites that are REE enriched with variable LREE/HREE ratios (Fig. 4). Although these rhyolites have been the focus of geological and geochemical research, very few have been examined from an economic geology viewpoint, let alone considering their potential for REE extraction. Key areas that need to be addressed in any further research into the REE potential of these (and other) rhyolites are their textures (e.g.

Many of the rhyolites discussed above are missing the full set of REE concentrations, primarily as previous research did not always routinely analyse the full set of the REE. As such, we focus on Yb, a more valuable HREE and one of the elements whose concentrations were determined for the vast majority of the rhyolites discussed here, allowing us to compare these rhyolites to each another and to other known REE ore deposits. Here, we use the NI43-101 certified Round Top deposit as the type

Skinners classic 1976 paper formalised the mineralogical barrier concept for geochemically scarce metals (Fig. 7) and outlined the importance of mineralogy to mineral processing and the economic recovery of metals (Skinner, 1976). This concept indicates that a point exists when energy costs make extraction of a given metal from a given mineral or minerals prohibitively expensive (for example Ni from olivine), an extremely important consideration in terms of discussing the economic potential

Price et al. (1990) and others have suggested that late stage magmatic-hydrothermal vapour phase crystallisation affected the Round Top rhyolite deposit and that this process may have caused some of the extreme HREE-enrichments present within this rhyolite. In addition, London et al. (1988) demonstrated that the HREE are more soluble in a vapour phase than the LREE, suggesting that this process could be responsible for sufficient enrichment and concentration of HREE to upgrade a rhyolite to

High-silica rhyolites with A-type geochemical affinities tend to form in extensional tectonic environments with sustained high heat flow (Bonin, 2007, Dall'Agnol et al., 2012, Medlin et al., 2015, Smithies et al., 2015, Whalen et al., 1987). The REE-enriched rhyolites discussed here represent the most evolved suites or units within an area, favouring a model whereby REE- and HREE-enrichment is related to extended fractionation. In addition, the correlation between high-F contents and

Highly fractionated REE-enriched rhyolites have the potential to be the bulk-tonnage, low-grade porphyry Cu deposits of the REE world. The fact that the magmatic processes that form these rhyolites can lead to HREE enrichments during extended fractionation combined with the generally favourable host mineralogy of deposits such as Round Top means that these rhyolites may be an important future source of the REE and especially the HREE. It is possible that late stage magmatic processes such as

The Ngaanyatjarra Council and their people are thanked for the privilege of working in their shire and providing a unique opportunity to work on these rocks. We acknowledge the Geological Survey of Western Australia (GSWA), especially R. H. Smithies, for funding and logistical support and the Monash Volcanology Research Group (MonVolc) for research collaboration and additional funding. We thank Kathryn Goodenough and an anonymous reviewer for constructive comments that much improved the paper

Rare earth elements (REEs), a group of 17 elements comprises 15 lanthanides, scandium and yttrium, are largely attracting the worlds attention due to their importance in a wide variety of advanced technological applications. Global REEs production is mainly sourced from resources, such as carbonatites, alkaline igneous rocks, placers, laterites, and ion-adsorption clays. Recently, REE demand has been escalating, especially due to the REE applications in renewable energy and defense sectors, expecting a worldwide shortage of REE supply in the future. Therefore, REEs have been widely accepted as strategic elements in the world, which compels to prospect for new and alternative REE resources. In this context, Sri Lanka has a favorable geological setting which implies the presence of REE mineralization. Previous geochemical studies in Sri Lanka have reported significant concentrations of REEs in different geological formations and mineral resources. Accordingly, Pulmoddai and other beach placer deposits, Eppawala carbonatite, alluvial placer deposits, and pegmatites have been identified as potential REE resources in Sri Lanka. Monazite, apatite, allanite, and zircon are the primary rare earth (RE) minerals found in the preceding resources. The Pulmoddai mineral sand deposit is considered as the most potential REE resource in the island, which is enriched in monazite containing more than 61% of light rare earth elements (LREEs). Similarly, Eppawala carbonatite contains high concentrations of LREEs. However, despite their significant REE enrichments, to date, no attempt has been made to recover these REE prospects, which essentially conceals their potential of catering for both local and global REE supply chains.

The Oligocene Peak Range Volcanics (PRV) of central Queensland have intruded through, and erupted onto, Permian sedimentary rocks of the Bowen Basin above what is likely to be a lithospheric-scale suture zone. The southern PRV consists of domes and flows of augite (bearing) trachyte, hornblende trachyte, hornblende rhyolite, arfvedsonite rhyolite and aegirine rhyolite. The aegirine rhyolite bodies represent the most evolved rock types, with peralkaline index (molar Na+K/A) values of >1.3 and extreme enrichment in trace elements, including the rare metals Zr, Hf, Nb, Ta, and REE. Clarrys Dome, one of three aegirine rhyolite domes, features a late stage magmatic agpaitic assemblage of dalyite (K2ZrSi6O15), a eudialyte-like mineral and aegirine, which is variably replaced and overprinted by secondary REE carbonates and Zr silicates.

Major and trace element geochemistry are used to show that the suite of PRV rock types represent a fractionation sequence from the least evolved augite trachytes to the most evolved aegirine rhyolites. This rock type range can be modelled by extended alkali-feldspar-dominated fractional crystallisation of an alkali basalt parental melt at a shallow crustal levels. Initial Nd values across the range of rock types are between +3 to +4, which is consistent with a common mantle source. Thus, the extreme trace element enrichment and high peralkalinity of the aegirine rhyolites is the product of the extended fractionation of a melt formed by low-degree partial melting of a mildly depleted mantle source. The secondary ore mineral assemblage and REE redistribution observed in the core of Clarrys Dome is interpreted to be due to a combination of hydrothermal alteration by fluids derived from subjacent devolatilising magma bodies, and late-stage weathering.

The extreme enrichment of rare metals in the aegirine rhyolite bodies in the southern PRV support their potential to represent low grade, but large tonnage (100s of Mt) resources of rare metals. Clear evidence of hydrothermal alteration across the region also raised the potential that higher grade rare metal mineralisation produced by hydrothermal activity may exist in the region.

In some cases, the felsic volcanic rocks associated with limited ion adsorption-type REE deposits (i.e., those of Jingningian (1000850 Ma) and late Yanshanian (11665 Ma) ages) do have high REE concentrations.For example, REE concentrations of Jingningian felsic volcanic rocks vary from 82 to 821 ppm (e.g., Lu and Gu, 2007; Lu et al., 2009; Jowitt et al., 2017), and those of late Yanshanian age range from 132 to 482 ppm (Wang and Ruan, 1989; Lu, 1997; Zhou, 2007).Hence, the main reason for the scarcity of ion adsorption-type REE mineralization in these two felsic volcanic rock weathered terrains is likely associated with factors other than the nature of the parent rock.

Felsic volcanic rocks are an important source for generating ion adsorption-type rare earth element (REE) resources. To better understand the supergene enrichment of REEs related to felsic volcanic rock weathering, this study conducted an investigation of Indosinian felsic volcanic rocks from Guangxi, southwest China, which have been subjected to deep weathering. The weathering has formed large areas of thick regolith with the potential to host ion adsorption-type REE mineralization. The felsic volcanic rocks belong to the daciterhyolite series and are peraluminous, high-K, calc-alkaline, and REE-rich (325376ppm). Abundant REE-bearing accessory minerals are present in the felsic volcanic rocks, including titanite (average REE=15.1wt%), allanite (average REE=14.9wt%), and apatite (average REE=1510ppm), and these three minerals contain an estimated 88.7% of the whole-rock REEs content. Significant REE enrichment is present in the felsic volcanic rock-derived regolith. A typical rhyolite-derived regolith profile has REE contents that increase from 376ppm in the rhyolite to 1737ppm in the regolith, representing an almost five-fold enrichment due to weathering. The REEs in the regolith are present in an ion-exchangeable form (iREEs), which accounts for 52%87% of the total REEs present (TREEs). The occurrence of iREEs is closely linked to clay minerals, showing an affinity in the order halloysite>kaolinite>illite. Continuous operations of REEs by an eluviationilluviation process from the source minerals (titanite+allanite+apatite) to sink minerals (kaolinite+halloysite+illite) results in an iREE-enriched zone in the middle and lower parts of the rhyolitic regolith. Notably, besides the studied Indosinian felsic volcanic rocks, there are multi-epochs of such lithology outcropped in South China. Their related iREEs mineralizations, however, are preferentially developed in the weathered terrains of early Yanshanian and Indosinian felsic volcanic rocks, and not in those of the Yanshanian and late Yanshanian felsic volcanic rocks. A comparison of the mineralized and barren units indicates that the iREEs mineralization hosted in felsic volcanic rocks regolith is controlled by some key endogenic and exogenic ore-forming factors. High initial REE concentrations in the unaltered felsic volcanic rocks, a suitable climate, and a relatively quiescent tectonic setting are favorable for the formation and preservation of iREEs mineralization.

Therefore, most of the key outcrops appear in protected areas, where extractive operations are prohibited and mining is not viable.Our geochemical exploration study confirmed that the felsic magmatic rocks (phonolites, trachytes, rhyolites and syenites) and the associated paleosols of Gran Canaria can be considered to be a type of low-grade and bulk tonnage ore deposit for oceanic, intraplate volcanic islands, similar to that described by Jowitt et al. (2017) for highly fractionated rhyolites.The total volume of the felsic rocks in the alkaline declining stage (emitted between 14.1 and 7.3 Ma) is approximately 1000 km3 (Schmincke, 1976, 1982; Schmincke and Sumita, 2010) and, assuming that these rocks have a density of 2700 kg m3, this yields 2700 MT. Taking into account the mean 672 mg kg1 REE grade in this alkaline stage, the total tonnage of REE on Gran Canaria would be about 1814 MT of potential REE resources.

Gran Canaria is a hotspot-derived, intraplate, oceanic island, comprising a variety of alkaline felsic magmatic rocks (i.e. phonolites, trachytes, rhyolites and syenites). These rocks are enriched in rare-earth elements (REE) in relation to the mean concentration in the Earth's crust and they are subsequently mobilised and redistributed in the soil profile. From a set of 57 samples of felsic rocks and 12 samples from three paleosol profiles, we assess the concentration and mobility of REE. In the saprolite that developed over the rhyolites, we identified REE-bearing minerals such as primary monazite-(Ce), as well as secondary phases associated with the edaphic weathering, such as rhabdophane-(Ce) and LREE oxides. The averaged concentration of REE in the alkaline bedrock varies from trachytes (449mgkg1), to rhyolites (588mgkg1) and to phonolites (1036mgkg1). REE are slightly enriched in saprolites developed on trachyte (498mgkg1), rhyolite (601mgkg1) and phonolite (1171mgkg1) bedrocks. However, B-horizons of paleosols from trachytes and phonolites showed REE depletion (436 and 994mgkg1, respectively), whereas a marked enrichment was found in soils developed on rhyolites (1584mgkg1). According to our results, REE resources on Gran Canaria are significant, especially in Miocene alkaline felsic magmatic rocks (declining stage) and their associated paleosols. We estimate a total material volume of approximately 1000km3 with REE concentrations of 672296mgkg1, yttrium contents of 5730mgkg1, and light and heavy REE ratios (LREE/HREE) of 176. This mineralisation can be considered as bulk tonnage and low-grade ore REE deposits but it remains necessary to develop detailed mineral exploration on selected insular zones in the future, without undermining environmental and socioeconomic interests.

Therefore, the flowing direction of injecting aqueous solution in in-situ leaching process can be determined by the spatial fractionation characteristics of IARE, and used to design specific in-situ leaching solutions for increasing leaching efficiency (LE) and decreasing pollutant emissions.4The fractionation of REs refers to the apparent difference in partition values (PVs, the ratio of various individual REs to total RE content) of REs at different locations in a deposit due to the difference in RE migration ability caused by the slight property variation of individual RE.1,2,1824It is believed that the fractionation of IARE is caused by numerous adsorption-desorption and migration processes of RE ions between natural flowing water and clay minerals, and is often used as a probe to study the metallogenic mechanism.4

The fractionation of ion adsorption rare earths (IAREs) along the depth in a shaft of a deposit at Dajishan, Jiangxi, China was comparatively evaluated using the partition values (PVs) and relative fractionation values (RFVs) of the leached rare earths (REs). It is found that both PVs and RFVs can objectively reflect the migration and fractionation of REs, but RE content and abrasion pH could not. However, the RFVs can provide more information to quantitatively evaluating the migration and fractionation characteristics of REs along the selected direction and region than PVs could, which is of significance for designing the optimal procedures of in-situ leaching based on the determined flow direction of injecting solution. It is demonstrated that the migration of Ce, Pr, and Nd along the depth direction is inert, and that of REs post Sm and Y is active. Meanwhile, the migration of La shows region characteristics which is active in the upper and inert in lower region. More interesting, the dependence of RFVs on atomic number of REs displays a tetrad group variation trend. However, the fractionation of REs among clay minerals with different particle sizes is not evident, especially for the clay in the bottom region. These results indicate that the migration and fractionation of REs not only are dominated by the adsorption of their hydrated ions, but also rely on their hydrolysis tendency, which provide information for understanding the metallogenic mechanism of IAREs.

One of the most puzzling features of the UG1 chromitite layers in the famous exposures at Dwars River, Eastern Bushveld Complex, is the bifurcation, i.e. convergence and divergence of layers along strike that isolate lenses of anorthosite. The bifurcations have been variously interpreted as resulting from: (1) the intermittent accumulation of plagioclase on the chamber floor as lenses, terminated by crystallization of continuous chromitite layers (the depositional model); (2) late-stage injections of chromite mush or chromite-saturated melt along anastomosing fractures that dismembered semi-consolidated plagioclase cumulates (the intrusive model); (3) post-depositional deformation of alternating plagioclase and chromite cumulates, resulting in local amalgamation of chromitite layers and anorthosite lenses that wedge out laterally (the deformational model). None of these hypotheses account satisfactorily for the following field observations: (a) wavy and scalloped contacts between anorthosite and chromitite layers; (b) abrupt lateral terminations of thin anorthosite layers within chromitite; (c) in situ anorthosite inclusions with highly irregular contacts and delicate wispy tails within chromitite; many of these inclusions are contiguous with footwall and hanging wall cumulates; (d) transported anorthosite fragments enclosed by chromitite; (e) disrupted anorthosite and chromitite layers overlain by planar chromitite; (f) protrusions of chromitite into underlying anorthosite; (g) merging of chromitite layers around anorthosite domes. We propose a novel hypothesis that envisages basal flows of new dense and superheated magma that resulted in intense thermo-chemical erosion of the temporary floor of the chamber. The melting and dissolution of anorthosite was patchy and commonly inhibited by chromitite layers, resulting in lens-like remnants of anorthosite resting on continuous layers of chromitite. On cooling, the magma crystallized chromite on the irregular chamber floor, draping the remnants of anorthosite and merging with pre-existing chromitite layers excavated by erosion. With further cooling, the magma crystallized chromite-bearing anorthosite. Emplacement of multiple pulses of magma led to repetition of this sequence of events, resulting in a complex package of anorthosite lenses and bifurcating chromitite layers. This hypothesis is the most satisfactory explanation for most of the features of this enigmatic igneous layering in the Bushveld Complex.

Retrograde hydrous metamorphism has produced three types of microstructures in chromite grains from chromitites and enclosing rocks of the Tapo Ultramafic Massif (Central Peruvian Andes). In semi-massive chromitites (6080vol% chromite), (i) partly altered chromite with homogeneous cores surrounded by lower Al2O3 and MgO but higher Cr2O3 and FeO porous chromite with chlorite filling the pores. In serpentinites (ii) zoned chromite with homogeneous cores surrounded by extremely higher Fe2O3 non-porous chromite and magnetite rims, and (iii) non-porous chromite grains. The different patterns of zoning in chromite grains are the consequences of the infiltration of reducing and SiO2-rich fluids and the subsequent heterogeneous interaction with more oxidizing and Fe-bearing fluids. During the first stage of alteration under reduced conditions magmatic chromite is dissolved meanwhile new metamorphogenic porous chromite crystallizes in equilibrium with chlorite. This reaction that involves dissolution and precipitation of minerals is here modeled thermodynamically for the first time. SiO2-MgO pseudosection calculated for unaltered semi-massive chromitites at 2kbar and 300C, the lowest P-T conditions inferred from the Tapo Ultramafic Massif and Maran Complex, predicts that chromite+chlorite (i.e., partly altered chromite) is stable instead of chromite+chlorite+brucite at progressive higher SiO2 but lower MgO. Our observation is twofold as it reveals that the important role of SiO2 and MgO and the open-nature of this process. P-T-X diagrams computed using the different P-T pathways estimated for the enclosing Tapo Ultramafic Massif reproduce well the partial equilibrium sequence of mineral assemblages preserved in the chromitites. Nevertheless, it is restricted only to the P-T conditions of the metamorphic peak and that of the latest overprint. Our estimations reveal that a high fluid/rock ratio (1:40 ratio) is required to produce the microstructures and compositional changes observed in the chromitites from the Tapo Ultramafic Massif. The circulation of SiO2-rich fluids and the mobilization of MgO from the chromitite bodies are linked with the formation of garnet amphibolites and carbonate-silica hydrothermalites (i.e., listwaenites and birbirites) in the ultramafic massif. The origin of these fluids is interpreted as a result of the dissolution of orthopyroxene and/or olivine from the metaharzburgites and metagabbros enclosed in the Tapo Ultramafic Massif.

The Seligdar apatite deposit is located in the Aldan-Stanovoy shield of the Siberian platform in Russia. This deposit is a typical ore deposit of the Nimnyrskaya approximately N-S apatite zone, which is about 400km long. The genesis of the apatite-dolomite ores at the Seligdar deposit is a matter of debate. This article presents new evidence of the carbonatitic genesis of the apatite-dolomite rocks at the Seligdar deposit based on modern methods of mineralogical, geochronological, melt and fluid inclusion investigations. According to our data, the age of the apatite-dolomite ores is 188013Ma (U-Pb SHRIMP, zircon). Study of melt inclusions indicates that the ores were formed from a carbonate melt of dolomitic composition with alkali (sulphates, chlorides and fluorides of Na and K) and silica components (110wt.%) at a temperature of >1100C. The dolomite carbonatites have been subsequently exposed to the intense processes of hydrothermal-metasomatic alteration and metamorphism. The evolution of mineral parageneses from the magmatic apatite-magnetite-dolomite carbonatite stage to the hydrothermal stages with quartz, calcite, monazite-Ce, xenotime-Y, haematite, thorite, thorianite, sulphates and sulphides mineralization agrees with the fluid inclusion regime evolution from the carbonate melt to the chloride brines, and the varying concentrations of the chloride solutions are also described in this article. The investigation of the apatite deposits within the Aldan shield not only allows us to take a new look at the question of their origin but also helps us to study the composition of the ancient mantle, as well as the specifics of apatite-dolomite carbonatite and related hydrothermal Fe and Th-REE mineralization in this region.

Apatite-group phosphates are nearly ubiquitous in carbonatites, but our understanding of these minerals is inadequate, particularly in the areas of element partitioning and petrogenetic interpretation of their compositional variation among spatially associated rocks and within individual crystals. In the present work, the mode of occurrence, and major- and trace-element chemistry of apatite (sensu lato) from calcite and dolomite carbonatites, their associated cumulate rocks (including phoscorites) and hydrothermal parageneses were studied using a set of 80 samples from 50 localities worldwide. The majority of this set represents material for which no analytical data are available in the literature. Electron-microprobe and laser-ablation mass-spectrometry data (~600 and 400 analyses, respectively), accompanied by back-scattered-electron and cathodoluminescence images and Raman spectra, were used to identify the key compositional characteristics and zoning patterns of carbonatitic apatite. These data are placed in the context of phosphorus geochemistry in carbonatitic systems and carbonatite evolution, and compared to the models proposed by previous workers. The documented variations in apatite morphology and zoning represent a detailed record of a wide range of evolutionary processes, both magmatic and fluid-driven. The majority of igneous apatite from the examined rocks is Cl-poor fluorapatite or F-rich hydroxylapatite (0.3apfu F) with 0.22.7wt.% SrO, 04.5wt.% LREE2O3, 00.8wt.% Na2O, and low levels of other cations accommodated in the Ca site (up to 1000ppm Mn, 2300ppm Fe, 200ppm Ba, 150ppm Pb, 700ppm Th and 150ppm U), none of which show meaningful correlation with the host-rock type. Silicate, (SO4)2 and (VO4)3 anions, substituting for (PO4)3, tend to occur in greater abundance in crystals from calcite carbonatites (up to 4.2wt.% SiO2, 1.5wt.% SO3 and 660ppm V). Although (CO3)2 groups are very likely present in some samples, Raman micro-spectroscopy proved inconclusive for apatites with small P-site deficiencies and other substituent elements in this site. Indicator REE ratios sensitive to redox conditions (Ce, Eu) and hydrothermal overprint (Y) form a fairly tight cluster of values (0.81.3, 0.81.1 and 0.60.9, respectively) and may be used in combination with trace-element abundances for the development of geochemical exploration tools. Hydrothermal apatite forms in carbonatites as the product of replacement of primary apatite, or is deposited in fractures and interstices as euhedral crystals and aggregates associated with typical late-stage minerals (e.g., quartz and chlorite). Hydrothermal apatite is typically depleted in Sr, REE, Mn and Th, but enriched in F (up to 4.8wt.%) relative to its igneous precursor, and also differs from the latter in at least some of key REE ratios [e.g., shows (La/Yb)cn25, or a negative Ce anomaly]. The only significant exception is Sr( REE,Na)-rich replacement zones and overgrowths on igneous apatite from some dolomite(-bearing) carbonatites. Their crystallization conditions and source fluid appear to be very different from the more common Sr-REE-depleted variety. Based on the new evidence presented in this work, trace-element partitioning between apatite and carbonatitic magmas, phosphate solubility in these magmas, and compositional variation of apatite-group minerals from spatially associated carbonatitic rocks are critically re-evaluated.

Preliminary mineralogical and geochemical studies have been carried out on dolomite marble drill cores from the Bayan Obo REE deposit in China. Three types of apatites and four types of monazites have been identified based on textural features: Type 1 apatite occurs as grains with minor monazite (Type 1 monazite) on its border; Type 2 apatite veinlet shows clusters of assemblages with abundant bastnsite and parisite at the rim; Type 3 apatite has a linear array associated with fluorite and bastnsite veinlets. Type 2 monazite occurs as clusters intergrowing with parisite and fluorite. Type 3 and 4 monazites occur as polymineralic (fluorite and bastnsite) and monomineralic veinlets, respectively. These four types of monazites have similar LREE composition but variable Y content (Y2O3 ranging from below determination limits to 0.7wt%). The three types of apatites also show different REE content and distribution patterns, ranging from high REE abundance (REE+Y: 27243251789ppm) and strong LREE enrichment [(La/Yb)CN 101] in Type 1, less LREE enrichment [(La/Yb)CN 8] in Type 2 to relatively low REE abundance (REE+Y: 432311175ppm) but high REE fractionation [(La/Yb)CN 58] in Type 3. The primary apatite has high Sr (54616892ppm) and REE content, implying a carbonatite origin. The late-stage apatites (Types 2 and 3) show different Sr and REE abundances. Significant differences in their Sr composition (6189573, 6041549 and 3492802 for Types 13 samples, respectively) and Y/Ho ratio (20.90.11, 19.50.17 and 17.40.37, respectively) indicate that the three types of apatites may have crystallized from different metasomatic fluids. Multi-stage metasomatism resulted in remobilization and redeposition of primary REE minerals to form the Bayan Obo REE deposit.

The MianningDechang (MD) REE belt of Sichuan, China is one of the most important REE belt in China, which includes Maoniuping, the third largest REE deposit in the world and a series of large to small REE deposits. Mineralization styles varied across the belt, as well as within different parts of the same deposit. Styles include vein-stockworks, pegmatites, breccias and disseminated REE mineralization. Based on geological, geochemical and inclusion studies, this paper proposes a new model for carbonatite hosted REE mineralization. The results show that ore-forming fluid is derived from carbonatite magma, which has high temperature, pressure and density, and is characterized by high K, Na, Ca, Sr, Ba, REE and SO4 contents. The supercritical ore fluid underwent a distinctive evolution path including phase separation, exolution of sulfate melt and unmixing between aqueous fluid and liquid CO2. Rapid geochemical evolution of a dense carbonatite fluid causes REE mineralization and associated alteration to occur within or proximal to the source carbonatite. Veins, pegmatites and carbonatite comprise a continuum of mineralization styles. Veins occur in the outer zone of the upper levels of the deposit. Pegmatites occur in the inner zone of upper levels, whereas disseminated REE ore occurs at the base of the carbonatite. High water solubility in the carbonatite magma and low water, high REE in the exsolved ore-forming fluids, imply that a giant carbonatite body and deep magma chamber are not necessary for the formation of giant REE deposits.

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